Information

Diet

The
Importance of Diet in RabbitsAnna Meredith
MA VetMB CertLAS DZooMed MRCVS
Head of Exotic Animal Service Royal (Dick) School of
Veterinary Studies University of Edinburgh

Feeding an appropriate diet to a rabbit is probably
the single most important factor in maintaining its
health. Rabbits are now the third most popular mammalian
domestic pet in the UK. They are also an extremely important
livestock species and laboratory model worldwide. There
is a great deal of literature relating to the nutrient
requirements of production and laboratory rabbits, but
relatively little relating specifically to the pet rabbit.
Pet rabbits have the potential for a much longer lifespan
than the short-lived production or experimental rabbit.
Many of the diseases commonly seen in pet rabbits can
be directly attributed to, or associated with, the feeding
of an inappropriate diet and could be largely preventable.
However, in recent years manufacturers have responded
to the need for good diets for pet rabbits, and in general
the level of awareness of all those involved with keeping
pet rabbits has increased.

When considering the diet of a pet rabbit it is
important to be aware of the dietary habits of the
wild rabbit. Rabbits are adapted in terms of their
teeth and digestive system to eat a herbaceous diet
that is high in fibre, low in fat, and low in starchy
carbohydrates. Wild rabbits in a natural setting select
the most tender succulent plant parts that are most
nutrient dense. They are referred to as concentrate
selectors, allowing them to meet their dietary requirements
in the minimum time above ground when they are prone
to predation. However, the natural diet is not "concentrated"
to the same degree as commercial diets and is still
naturally high in fibre.

Pet rabbits will generally eat a wide variety of
foods but generally show a preference for fibre and
often eat hay or straw in preference to a concentrate
ration. However, it can be difficult to persuade a
rabbit to eat a new food item once it has become accustomed
to a particular diet. Food preference is influenced
by the diet of the mother at weaning. Rabbit kits
show a clear preference for the diet of their mother
at weaning. It can be particularly difficult to persuade
some rabbits to eat hay if they have not been introduced
at an early age. In the wild rabbits eat at dusk and
dawn, and this is reflected in pet rabbits, that are
most likely to eat in the early evening or overnight,
and may not appear hungry during the day.

The other source of nutrients is the caecotrophs,
which are packets of partially digested food and bacterial
products, including vitamins, eaten directly from
the anus. The amount of caecotrophs eaten is affected
by energy and protein levels in the diet. If the diet
is energy deficient, rabbits will consume all the
produced caecotrophs. During ad libitum feeding, caecotroph
intake depends on the protein and fibre content of
the diet, being greater if the diet is lower in protein
or higher in fibre.

Sweet foods are generally palatable and molasses
is used in some commercial foods to improve palatability.
Bitter tastes are also well tolerated, such as alfalfa
.

LINKS BETWEEN DIET AND DISEASE

Low fibre and high carbohydrate diets are linked
to dental disease, gastrointestinal disease, obesity
and behavioural problems. Excess calcium in the diet
can be linked to urolithiasis (bladder stones).

1. Dental disease Rabbit teeth grow constantly throughout
life. The rate of growth should balance the amount
of wear produced by grinding fibrous foods, so that
tooth length stays constant. Incisor wear, growth
and eruption are balanced in a normal rabbit at a
rate of about 3mm per week. Food is ground by the
cheek teeth. A natural diet of grass and plants is
highly abrasive to the cheek teeth, so there is rapid
wear of the teeth, around 3mm per month, with equally
rapid tooth growth. Upper teeth grow faster than lower
teeth, which is why problems are generally seen first
on the upper jaw.

Rabbits on a high carbohydrate and low fibre diet
have reduced tooth wear and therefore elongation of
the tooth both above and below the gum. This results
in irregular wear, distortion and the formation of
sharp painful spikes. Severe elongation of the cheek
teeth can prevent the mouth from closing fully, which
ultimately prevents the incisors meeting properly,
causing them to also overgrow. Overgrown distorted
teeth are predisposed to infection and the development
of facial abscesses.

High carbohydrate diets and reduced wear also predispose
to caries (cavities).

Opinions vary on the significance of dietary calcium
levels on dental disease. Many rabbits are selective
eaters of coarse mix, favouring items low in calcium
and fibre. This can make them prone to osteoporosis,
poor tooth and bone quality, and dental disease. Bone
growth, development and maintenance is also dependent
on the mechanical stresses to which it is subjected
and rabbits which do not spend prolonged periods grinding
fibrous food can also show poor jaw bone quality.
Low vitamin D levels are common in rabbits that have
no access to sunlight, and this may also be associated
with poor tooth and bone quality. Although rabbits
do not need vitamin D in order to absorb calcium,
low levels of both calcium and vitamin D are likely
to be a significant factor in the progression of dental
disease.

Not all dental disease is due to diet, and genetic
factors are also important. A congenital malalignment
of the teeth, particularly in extreme dwarf and lop
breeds, can also be a significant factor.

2. Gastrointestinal disease Fibre is critical to
the rabbit for gastrointestinal health because it
stimulates and maintains normal motility of the gut.
Low fibre diets predispose to gut stasis and the formation
of hairballs. Carbohydrates (simple sugars and starches)
are an important energy source and are digested and
absorbed in the stomach and small intestine. However,
any residual starch that is not digested and absorbed
in the small intestine passes into the caecum as a
substrate for bacterial fermentation. High starch
diets can be incompletely digested due to the rapid
gut transit times, and cause a rapid overgrowth in
caecal bacteria. This can lead to enterotoxaemia and
a fatal diarrhoea. This is seen mainly in young, recently
weaned rabbits when also fed minimal hay, and combined
with the stress of a change of diet and a recent move,
for example from a breeder to a pet-shop.

3. Behavioural problems Rabbits in the wild spend
many hours a day eating. Low fibre concentrate diets
are rapidly eaten and rabbits can develop vices related
to boredom, such as increased aggression or repetitive
bar biting. Lack of fibre can also lead to fur chewing
and barbering.

4. Obesity Fats are used in commercial rabbit diets
to improve palatability and provide a non-carbohydrate
energy source. Fat also stimulates gastrointestinal
motility, but reduces intestinal absorption of calcium.
Many treat foods contain high levels of fat, (e.g.
chocolate drops) and should not be fed. High fat levels
also increase the risk of hepatic lipidosis developing
during periods of starvation. Pet rabbits are prone
to obesity so high fat diets and ad lib feeding of
concentrates should be avoided.

5. Urolithiasis Excess calcium in the diet can contribute
to sludgy urine or even urolithiasis (bladder stones),
which often require surgical treatment. Rabbits have
a unique calcium metabolism in that they do not control
uptake of calcium from the gut. Instead, they absorb
most of what is eaten and excrete the excess in the
form of calcium carbonate, in the urine. Although
it is normal for rabbits to have calcium crystals
in the urine, overweight inactive animals, those with
neurological or other problems affecting normal bladder
function and emptying, or those with urinary tract
infections seem predisposed to developing problems
associated with this.

Substances in foods called phytates, oxalates and
acetates form complexes with calcium and other minerals
and this can hinder their absorption. Phytic acid
is present in high quantities on grains and beans.
Oxalates are present in many plants including swede,
spinach and alfalfa, in which 20-30% of the calcium
is in the form of calcium oxalate which reduces its
availability. Feeds high in calcium and low in oxalate
include kale, broccoli, turnip, collard and mustard
greens.

DIETARY ITEMS

GRASS AND HAY

Grass provides a balanced source of protein, digestible
and indigestible fibre, vitamins and minerals, and
ideally pet rabbits should be allowed to graze for
several hours a day. However this can be impractical
for house rabbits. Grass is approximately 20 - 40%
crude fibre. Grass should be grazed or fed fresh cut.
Lawnmower clippings should not be used as they ferment
rapidly and can cause digestive disturbance.

Hay should also be considered an essential part
of the pet rabbit diet and should be provided ad libitum.
Hay can be used as a substitute for grass, or fed
in addition. Species of grass used for haymaking in
the UK are ryegrass, timothy, fescues, meadow grass,
and Cocksfoot (orchard grass) and are generally referred
to as meadow hay, often containing a mixture of species,
including come clover. Fibre content varies from 29.8%
(meadow grass) to 35.6% (orchard grass). Protein content
of grass hays is generally in the range 6.3% to 16.7%.
Quality will vary depending on the time of year. Cutting
hay before flowering gives the best quality. Opinion
varies as to the best age of hay to feed. Some rabbit
keepers recommend feeding hay that is at least 4 months
old as young hay may lead to diarrhoea, but others
feed new hay with no problems. Prolonged storage of
hay can lead to loss of nutrients, especially vitamins
A and D, and especially if the temperature is warm.
Good hay is sweet-smelling and with no mustiness.
Lucerne (alfalfa) is used widely in the USA and other
parts of the world for haymaking but is not common
in the UK. It is high in protein (16.5%) and calcium
and is thus very useful for growing rabbits, but can
lead to obesity and urolithiasis in mature animals.
Other legume hays (e.g clover) are similarly high
in protein, calcium and energy and are not recommended
for adult pet rabbit.

Straw is not recommended as, although eaten, is
low in nutrients and will lead to deficiencies if
it is a major part of the diet.The feeding of silage
is generally not practical, although it has been approached
in some countries.

Anecdotal reports on the use of artificially dried
grass in rabbits have been received and rabbits seem
to find it very palatable. Nutrient content is often
superior to sun-dried hay, although vitamin D content
will be lower and carotene and vitamin E content can
deteriorate with time unless stored correctly.

MIXES, PELLETS AND EXTRUDED DIETS

Pet rabbit food has traditionally been sold in the
form of mixes consisting largely of flaked, micronised
or rolled cereals, legumes, extruded biscuits and
grass pellets. Alfalfa stems are sometimes included
to increase fibre content and as a calcium source.
More recently, pellets and extruded diets have been
made available for pet use, although pellets have
been used for many years for commercial production
rabbits

Harcourt-Brown (1996) found that pet rabbits offered
mixed diets tend to favour the flaked peas and maize
which are high in starch and low in calcium and fibre.
Locust beans are sometimes included as they are sweet
and palatable, but can be swallowed whole and cause
intestinal obstruction. Owners tend to discard uneaten
items and replenish the feeding bowl regularly so
that the complete balanced mixture of ingredients
is never consumed.

Pelleted or extruded diets overcome the problem
of selective feeding and provide a consistent ration.
Extruded diets are now very popular for pet rabbits,
incorporating long fibre particles without the pellet
becoming crumbly. The heated extrusion process improves
starch digestibility and reduces carbohydrate overload
of the hindgut, and extruded diets are more palatable
and digestible than pellets.

EDIBLE PLANTS

Plants can be either commercially available or wild.
Green leafy plants are recommended. Commercially available
examples are broccoli, cabbage, chicory, chard, parsley,
watercress, celery leaves, endive, raddichio, bok
choy, dock, basil, kale, carrot and beet tops. Wild
plants include bramble, dandelion, chickweed, plantain,
sunflower, wild strawberry, dock, yarrow. Green plants
are a useful to provide variety, micronutrients, water
and dental wear, but it should be remembered that
as they are generally 90-95% water and often relatively
low in fibre excessively large amounts would need
to be consumed to fulfil daily needs. Therefore they
should not be fed in very large quantities. Any greens
should be introduced gradually and preferably fed
consistently in order for caecal bacteria to adapt.

FOOD INTAKE

Many factors affect food intake, including size,
age, environmental temperature and reproductive status.
However, there is very little published information
for pet rabbits.

Although production rabbits may eat to meet their
energy requirements, this is not the case with many
pet rabbits that frequently overeat and become overweight
or obese. Conversely, if very low protein and high
fibre diets are fed, especially to small breeds, energy
intake may be limited and result in poor growth or
weight loss. Disease states usually increase energy
needs but decrease food intake. House rabbits kept
in warm ambient temperatures may require less energy
than outdoor rabbits, depending on their level of
activity. Neutered rabbits may also require less energy
due to reduced activity.

Growing rabbits should be expected to eat up to
twice the amount consumed by an adult and lactating
does three times the amount. In lactating does, energy
needs often exceed capacity for food intake and weight
will be lost.

CONCLUSIONS

Feeding the correct diet to rabbits is fundamental
to maintaining health, particularly of the dental
and digestive systems.

The best diet for rabbits is one that mimics
as closely as possible their natural grass-based
diet in the wild. Grass is approximately 20-25%
crude fibre, 15% crude protein and 2-3% fat. The
bulk of the diet of the pet rabbit should consist
of grass (fresh or freeze-dried) and/or good quality
meadow/Timothy hay, and this should be available
at all times. Hay can be fed from racks or nets
to minimise contamination and increase the time
spent feeding.

Green foods are also important and a variety
should be fed daily to rabbits of all ages. They
should be introduced gradually to weanling rabbits.
Examples are broccoli, cabbage, chicory, chard,
parsley, watercress, celery leaves, endive, raddichio,
bok choy, dock, basil, kale, carrot and beet tops.
Wild plants can be given if available, e.g bramble,
groundsel, chickweed, dandelion. All green foods
should be washed before feeding.

Commercial concentrate rabbit diets are not essential
in adult rabbits if ad lib hay, grass, and greens
are available. Commercial rabbit diets can be too
low in fibre and too high in protein, fat and carbohydrate
However, many owners like to feed these diets for
convenience. They should not be fed exclusively
or ad libitum, and it must be emphasised that hay
or grass should always be available and make up
the bulk of the diet. A good general rule is to
feed a maximum of 25g of high-fibre pellets per
kg bodyweight per day. For concentrate foods, crude
fibre levels of >18%, with indigestible fibre
>12.5% are recommended

Overfeeding of concentrated diets is a significant
factor in GI disease and dental disease, and also
leads to obesity and boredom. However, concentrate
diets have a role in the feeding of growing, pregnant
and lactating and diseased rabbits, and can be used
to ensure nutrient requirements are fulfilled in
rabbits that are unwilling to consume significant
amounts of hay or green vegetables.

High fat or high carbohydrate/starchy treats
should be avoided completely. These include commercial
"treats" such as honey sticks, beans, peas, corn,
bread, breakfast cereal, biscuits, nuts, seeds,
crisps and chocolate.

The best treats to feed are hay treats, which
are commercially available, or some favourite herbs
or greens. Be very careful with feeding other treats
as they can lead to obesity and digestive upsets.
For some tooth wear and mental stimulation you may
provide your rabbit with twigs or tree branches.
They will enjoy gnawing and stripping the bark.
A general rule is that you can offer branches from
any tree that we eat the fruit from. Examples are
apple, pear, plum, hawthorn, whitethorn and wild
rose. Make sure the tree has not been sprayed with
chemicals.

Fruit should be regarded as a treat item and
fed in limited quantities only as it is high in
simple sugars and can lead to gastrointestinal disturbance
and dental caries.

Sudden changes in diet must be avoided. Any change
in diet should be made gradually over several days
to weeks, starting with small amounts of the new
item and gradually increasing them, whilst making
a corresponding decrease in the unwanted item if
necessary. Ad lib hay should always be available,
and it is especially important to ensure that weanling
rabbits eat plenty of hay. A sudden change in diet
and lack of fibre combined with the stress of movement
is a significant cause of morbidity and mortality
in young rabbits over the period of weaning and
moving to a pet shop or new owner. When purchasing
a rabbit it is important for a new owner to be informed
of the rabbit's diet so that any changes can be
introduced gradually

Frosted or mouldy food, and lawnmower clippings
should not be fed as these can lead to severe digestive
disturbances.

Dietary supplements consisting of vitamins and
minerals are not generally necessary if the correct
diet is fed. They should be used only under direction
of a veterinary surgeon.

Fresh drinking water must be available at all
times. Drinking bottles are easier to keep clean
than water bowls, and avoid wetting the dewlap,
which can lead to a moist dermatitis

Table 1:

Nutrient requirements of pet rabbits

Protein - 12-16% (120-160g/kg)

Fibre - 20-25% (200-250g/kg)

Fat - 2.5-4% (25-40g/kg)

Vitamin A 10,000 IU/kg

Vitamin B complex B-group vitamin requirements
are supplied in sufficient quantity for pet rabbits
from caecotrophs. Diets for commercial production
rabbits are commonly supplemented with thiamine,
pyridoxine, riboflavin and niacin.

Vitamin D 1000 IU/kg

Vitamin E 0.05% (50mg/kg)

Calcium 0.5 - 1.0% (5-10g/kg)

Phosphorus - 0.4-0.8%. (4-8g/kg)

Magnesium 0.3% (3g/kg)

Zinc. 0.05% (50mg/kg)

Potassium 0.6% (6g/kg)

Sodium 0.2-0.25% (2-2.5g/kg)

Chloride 0.17-0.32% (1.7-3.2g/kg)

Iron 30-100 ppm

Copper 5-20 ppm

Manganese 8-15ppm

Selenium 0.05ppm

Iodine 0.4-2ppm

Cobalt 1.0 ppm

REFERENCES AND FURTHER READING

The Nutrition of the Rabbit. Ed de Blas and Wiseman.
CABI Publishing, Wallingford